The background description provided herein is for the purpose of generally presenting the context of the disclosure. Work of the presently named inventors, to the extent it is described in this background section, as well as aspects of the description that may not otherwise qualify as prior art at the time of filing, are neither expressly nor impliedly admitted as prior art against the present disclosure.
An engine combusts a mixture of air and fuel in a combustion process to produce a drive torque. During the combustion process, the engine converts chemical potential energy of the air/fuel mixture into kinetic energy and heat energy. A portion of the heat energy may be transferred to a coolant mass (m) circulating through the engine.
The heat energy may cause a coolant temperature of the coolant mass (m) to increase. The coolant temperature may be measured by an engine coolant temperature (ECT) sensor at a location inside the engine. The ECT sensor sends the ECT to an engine control module (ECM).
A thermostat may regulate the amount of the coolant mass (m) circulating through the engine. The thermostat is a thermostatic valve that opens when the coolant temperature reaches a thermostat opening temperature and closes when the coolant temperature is below the opening temperature. While the thermostat is closed, the coolant mass (m) circulating through the engine is smaller than when the thermostat is open.
Normally when the coolant temperature is below the opening temperature, the thermostat is closed so that the coolant mass (m) circulating through the engine is smaller. The heat energy transfers to the smaller coolant mass (m) and increases the ECT to an operating range. The operating range may be a coolant temperature range of approximately 180° F. to 200° F. Once the ECT is within the operating range, the thermostat may subsequently open to increase the amount of the coolant mass (m) circulating through the engine and regulate the coolant temperature.
A stuck open thermostat occurs when the thermostat remains stuck open regardless of the coolant temperature. The stuck open thermostat may delay or prevent the ECT from increasing to the operating range by allowing the coolant mass (m) circulating through the engine to be larger. The heat energy is transferred to a larger coolant mass, which results in a slower coolant temperature increase. The coolant temperature is therefore below the operating range for a longer period than when the coolant mass (m) is smaller.
While the coolant temperature is below the operating range, lubricating liquids inside the engine may be less effective and components of the engine may wear out faster. The combustion process may be less efficient and fuel vaporization may be less effective. The exhaust emissions may emit more pollutants. When the coolant temperature is in the operating range, the engine operates in more favorable conditions for fuel vaporization, engine lubrication, and exhaust emissions.
A coolant temperature model may be used to determine when the thermostat is stuck open. For example, a modeled ECT may be compared to the sensed ECT to determine when the thermostat is stuck open. When the difference between the modeled ECT and the sensed ECT is large enough, the thermostat may be stuck open. The model may be inaccurate and may require a lengthy period to diagnose the stuck open thermostat. In addition, multiple coolant temperature models may be required for multiple engines and cooling systems.